A little concerning that there so much death teenage lesbians, unless they just have been ghost for a long time, but still weird. Better to not think about it too much.
Interestingly, lovers' suicide was quite common during Japanese high-school girls at one point in Japan's history, since many of them fell in love with their classmates in all-girls' schools and couldn't deal with being whisked away at graduation to be pushed into obligatory het marriages. All those melodramatic, depressing Class S manga from the 80s and 90s were based, to an extent, in reality. I recommend watching Zeria's video series on the history of the yuri genre for more info.
Either that or these girls died while still being in the closet, and they're one regret was never kissing a girls, this leading them to being ghosts that can't move on until thry kiss a girl. This leads to a pretty upsetting theory that the pressure of staying in the closet was too much for them, leading to suicide. God, now I'm upset. I'm gonna go read some cute yuri